Evolutionary Patterns, Rates, and Trends

1. Evolutionary Patterns, Rates, and Trends Chapter 13

2. Asteroid Impacts Many past catastrophic impacts altered the course of evolution Iridium layer implicates asteroid in extinction of dinosaurs Asteroids are still a threat

3. Macroevolution The large-scale patterns, trends, and rates of change among families and other more inclusive groups of species

4. Fossils Recognizable evidence of ancient life What do fossils tell us? Each species is a mosaic of ancestral and novel traits All species that ever evolved are related to one another by way of descent

5. Stratification Fossils are found in sedimentary rock This type of rock is formed in layers In general, layers closest to the top were formed most recently

6. Fossilization Organism becomes buried in ash or sediments Organic remains become infused with metal and mineral ions Carbon 14 dating

7. Radiometric Dating

8. Geologic Time Scale Boundaries based on transitions in fossil record

9. Record Is Incomplete Fossils have been found for about 250,000 species Most species weren�t preserved Record is biased toward the most accessible regions

10. Continental Drift Idea that the continents were once joined and have since �drifted� apart Initially based on the shapes Later supported by world distribution of fossils and existing species, orientation of particles in iron-rich rocks

11. Plate Tectonics Earth�s crust is fractured into plates Movement of plates is driven by upwelling of molten rock at mid-oceanic ridges

12. Changing Land Masses

13. Comparative Morphology Comparing body forms and structures of major lineages Guiding principle: When it comes to introducing change in morphology, evolution tends to follow the path of least resistance

14. Morphological Divergence Change from body form of a common ancestor Produces homologous structures

15. Morphological Convergence Individuals of different lineages evolve in similar ways under similar environmental pressures Produces analogous structures that serve similar functions

16. Comparative Development Each animal or plant proceeds through a series of changes in form Similarities in these stages may be clues to evolutionary relationships Mutations that disrupt a key stage of development are selected against

17. Altering Developmental Programs Some mutations shift a step in a way that natural selection favors Small changes at key steps may bring about major differences Insertion of transposons or gene mutations

18. Developmental Changes Changes in the onset, rate, or completion of developmental steps can cause allometric changes Adult forms that retain juvenile features

19. Proportional Changes in Skull

20. Comparative Biochemistry Kinds and numbers of biochemical traits that species share is a clue to how closely they are related Can compare DNA, RNA, or proteins More similarity means species are more closely related

21. Comparing Proteins Compare amino acid sequence of proteins produced by the same gene Human cytochrome c (a protein) Identical amino acids in chimpanzee protein Chicken protein differs by 18 amino acids Yeast protein differs by 56

22. Sequence Conservation Cytochrome c functions in electron transport Deficits in this vital protein would be lethal Long sequences are identical in wheat, yeast, and a primate

23. Sequence Conservation

24. Nucleic Acid Comparison Use single-stranded DNA or RNA Hybrid molecules are created, then heated The more heat required to break hybrid, the more closely related the species

25. Molecular Clock Assumption: �Ticks� (neutral mutations) occur at a constant rate Count the number of differences to estimate time of divergence

26. Biological Species Concept �Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.� Ernst Mayr

27. Variable Morphology

28. Genetic Divergence Gradual accumulation of differences in the gene pools of populations Natural selection, genetic drift, and mutation can contribute to divergence Gene flow counters divergence

29. Genetic Divergence

30. Reproductive Isolation Cornerstone of the biological species concept Speciation is the attainment of reproductive isolation Reproductive isolation arises as a by-product of genetic change

31. Reproductive Isolating Mechanisms Prezygotic isolation Mating or zygote formation is prevented Postzygotic isolation Takes effect after hybrid zygotes form Zygotes may die early, be weak, or be sterile

32. Prezygotic Isolation Ecological isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic mortality

33. Postzygotic Mechanisms Zygotic mortality Hybrid inviability Hybrid sterility

34. Mechanisms of Speciation Allopatric speciation Sympatric speciation Parapatric speciation

35. Allopatric Speciation Speciation in geographically isolated populations Some sort of barrier arises and prevents gene flow Effectiveness of barrier varies with species

36. Extensive Divergence Prevents Inbreeding Species separated by geographic barriers will diverge genetically If divergence is great enough it will prevent inbreeding even if the barrier later disappears

37. Archipelagos Island chains some distance from continents Galapagos Islands Hawaiian Islands Colonization of islands followed by genetic divergence sets the stage for speciation

38. Speciation on an Archipelago

39. Hawaiian Islands Volcanic origins, variety of habitats Adaptive radiations: Honeycreepers: in absence of other bird species, they radiated to fillnumerous niches Fruit flies (Drosophila): 40% of fruit fly species are found in Hawaii

40. Speciation without a Barrier Sympatric speciation Species forms within the home range of the parent species Parapatric speciation Neighboring populations become distinct species while maintaining contact along a common border

41. Sympatric Speciation in African Cichlids Studied fish species in two lakes Species in each lake are most likely descended from single ancestor No barriers within either lake Some ecological separation but species in each lake breed in sympatry

42. Speciation by Polyploidy Change in chromosome number (3n, 4n, etc.) Offspring with altered chromosome number cannot breed with parent population Common mechanism of speciation in flowering plants

43. Possible Evolution of Wheat

44. We�re All Related All species are related by descent Share genetic connections that extend back in time to the prototypical cell

45. Patterns of Change in a Lineage Cladogenesis Branching pattern Lineage splits, isolated populations diverge Anagenesis No branching Changes occur within single lineage Gene flow throughout process

46. Evolutionary Trees

47. Gradual Model Speciation model in which species emerge through many small morphological changes that accumulate over a long time period Fits well with evidence from certain lineages in fossil record

48. Punctuation Model Speciation model in which most changes in morphology are compressed into brief period near onset of divergence Supported by fossil evidence in some lineages

49. Adaptive Radiation Burst of divergence Single lineage gives rise to many new species New species fill vacantadaptive zone Adaptive zone is �way of life� Cenozoic radiation of mammals

50. Extinction Irrevocable loss of a species Mass extinctions have played a major role in evolutionary history Fossil record shows 20 or more large-scale extinctions Reduced diversity is followed by adaptive radiation

51. Who Survives? Species survival is random tosome extent Asteroids have repeatedly struck Earth, destroying many lineages Changes in global temperature favor lineages that are widely distributed

52. Taxonomy Field of biology concerned with identifying, naming, and classifying species Somewhat subjective Information about species can be interpreted differently

53. Naming Species Each species has a two-part name First part is generic Second part makes it specific name Ursus arctos = brown bear Ursus americanus = black bear Bufo americanus = American toad

54. Higher Taxa Kingdom Phylum Class Order Family

55. Examples of Classification

56. Phylogeny The scientific study of evolutionary relationships among species Practical applications Allows predictions about the needs or weaknesses of one species on the basis of its known relationship to another

57. Six-Kingdom Scheme

58. Three-Domain Classification

59. Cladistics Organisms are grouped by shared derived traits Monophyletic group A group of species all descended from an ancestral species in which a particular derived trait first evolved

60. A Cladogram

61. Tree of Life